Nuclear Power Reactor Cooling Systems

The principal coolants which have been used for nuclear reactors are (1) liquids (e.g., water, heavy water, organic fluid), (2) gases (e.g., carbon dioxide, helium), and (3) liquid metals (e.g., sodium). 

The use of certain organic coolants, such as terphenyls, has been studied in some detail. These have the advantage of permitting operation at lower pressures, on account of their lower vapor pressure as compared with water. They have the additional advantage of being less corrosive than water at reactor temperatures. Their main disadvantage is a tendency to decompose under irradiation and high temperature. 

For gas-cooled reactors, the coolant which has been most widely used is carbon dioxide, which is readily available and has a low neutron absorption cross section. The poor heat transfer capability of a gas as compared to a liquid coolant requires the gas-cooled reactor to be operated at a high pressure (about 600 psi) in order to provide the required heat removal capacity. 

The third type of coolant, the liquid metal, has found its main use in the fast breeder reactor, where liquid sodium is the commonly accepted coolant, since water or organic liquids are ruled out because of their high moderating power. Sodium has the advantage of low moderation and neutron absorp- 

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US Code of Federal Regulations (2000b) Part 50.46 Acceptance Criteria for Emergency Cooling Systems for Light Water Nuclear Power Reactors , US Government. 

AR386 1.110 Cost-benefit analysis for radwaste systems for light-water-cooled nuclear power reactors... 

Japan imported its first commercial nuclear power reactor from the UK. Tokai-1, a 160 MWe gas-cooled (Magnox) reactor built by GEC. It began operating in July 1966 and continued until March 1998. Prior to the earthquake and tsunami of March 2011, and the nuclear disasters that resulted from it, Japan generated 30% of the country s electricity from its 50 nuclear reactors. The 2011 earthquake and tsunami caused the failure of cooling systems at the Fukushima I Nuclear Power Plant on March 11 and resulted in the closure of many of Japan s nuclear plants for safety inspections. The last of Japan s 50 reactors (Tomari-3) went offline for maintenance on May 5,2012, leaving Japan completely without nuclear-produced electrical power for the first time since 1970. 

Chapter 22 "Heat Transfer, Thermal Hydraulic, and Safety Analysis" and Chapter 23 "Thermodynamics and Power Cycles" are analytical tools used by engineers to evaluate reactor and power-producing systems. Heat transfer and thermal hydraulics are not only important in the operation of nuclear reactors, they are also critical in the evaluation of how the systems will respond under upset conditions. The chapter on thermodynamics is included to show how the energy generated by the reactor is transferred by the reactor cooling system to the turbine power generating system used to produce electricity. 

USNRC. 2014b. 50.46 Acceptance criteria for emergency core cooling systems for Ught-water nuclear power reactors. Available from http //www.nrc.gov/reading-rm/doc-collections/cfr/ part050/part050-0046.html (accessed on June 7,2014). 

American Nuclear Safety Transactions, June 1997. Volume 76, p.285, "Design evolution of emergency core cooling intake systems for US light water nuclear power reactors."... 

Passive safety systems based on natural circulation are intended to provide the ultimate heat sink in cases of failure of the normal operation of the reactor cooling system. Because of its critical importance, fundamental understanding of the properties and characteristics of namral-circulation hydrodynamics, thermal responses, and thermodynamics in the complex engineering equipment of nuclear reactor power systems is essential. For the Gen IV systems that are based on natural circulation at normal operating states the properties and characteristics under steady-state conditions must also be well understood. 

Acceptance Criteria for Emergency Core Cooling Systems for Light Water Cooled Nuclear Power Reactors, Title 10 Code of Federal Regulations Part 51.46, U.S. Atomic Energy Commission, Federal Register (January 4, 1974). 

The metal is a source of nuclear power. There is probably more energy available for use from thorium in the minerals of the earth s crust than from both uranium and fossil fuels. Any sizable demand from thorium as a nuclear fuel is still several years in the future. Work has been done in developing thorium cycle converter-reactor systems. Several prototypes, including the HTGR (high-temperature gas-cooled reactor) and MSRE (molten salt converter reactor experiment), have operated. While the HTGR reactors are efficient, they are not expected to become important commercially for many years because of certain operating difficulties. 

As previously stated, uranium carbides are used as nuclear fuel (145). Two of the typical reactors fueled by uranium and mixed metal carbides are thermionic, which are continually being developed for space power and propulsion systems, and high temperature gas-cooled reactors (83,146,147). In order to be used as nuclear fuel, carbide microspheres are required. These microspheres have been fabricated by a carbothermic reduction of UO and elemental carbon to form UC (148,149). In addition to these uses, the carbides are also precursors for uranium nitride based fuels. 

Nuclear power plant systems may be classified as "Frontline" and "Support. . iccurding to their. service in an accident. Frontline systems are the engineered safety systems that deal directly with an accident. Support systems support the frontline systems. Accident initiators are broadly grouped as loss of cooling accidents (LOCAs) or transients. In a LOCA, water cooling the reactor is lost by failure of the cooling envelope. These are typically classified as small-small (SSLOCA), smalt (SLOCA), medium (MLOCA) and large (LLOCA). 

Nuclear and magneto-hydrodynamic electric power generation systems have been produced on a scale which could lead to industrial production, but to-date technical problems, mainly connected with corrosion of the containing materials, has hampered full-scale development. In the case of nuclear power, the proposed fast reactor, which uses fast neutron fission in a small nuclear fuel element, by comparison with fuel rods in thermal neutron reactors, requires a more rapid heat removal than is possible by water cooling, and a liquid sodium-potassium alloy has been used in the development of a near-industrial generator. The fuel container is a vanadium sheath with a niobium outer cladding, since this has a low fast neutron capture cross-section and a low rate of corrosion by the liquid metal coolant. The liquid metal coolant is transported from the fuel to the turbine generating the electric power in stainless steel... 

The process at Three Mile Island involved nuclear fission and subsequent reactor cooling using circulating water. The primary water was kept under pressure to prevent boiling. Heat was transferred to a secondary water system that supplied power to a steam generator. Upon completion of this step, steam condensate was recovered and recycled. All radioactive materials, including primary water, were enclosed in a lined concrete containment building to prevent their escape to the atmosphere. 

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